For joining of an installation element—for example of a fitting or of a connecting piece—to a pipe by coldforming, the press tool is placed around a receiving part of the installation element. Drive forces are introduced into the press tool via a drive device, with the result that compressive forces are exerted by the press tool on the receiving part into which the pipe has been inserted. As a result of the compressive forces, the receiving part is formed in such a way that the receiving part is nondetachably joined to the inserted pipe by being pressed on.
As a rule, in addition to at least one press-on section for transmitting longitudinal and torsional forces, a receiving part also has a sealing section for sealing the joint, with the result that such a receiving part can be pressed onto a pipe to form a seal. In the case of joints of relatively small nominal diameters DN (Deutsche Norm [German standard]), a narrow impression region having a polygonal base shape is provided for mechanical securing of the joint.
The sealing of the joint between pipe and installation element is achieved, as a rule, by means of a gasket which faces the pipe and is arranged on the inside of the sealing section of the receiving part. For secure and reliable sealing, firstly an elastic compressive stress of the gasket, distributed uniformly all round, against the pipe and against the receiving part and, secondly, avoidance of crushing of the gasket are absolutely essential. Such a uniform compressive stress can be achieved only if, when the receiving part is being pressed on, the sealing section is formed uniformly all round within a very specific circumference. Manufacturers of such installation elements therefore specify shape tolerances predetermined in a type-specific manner, for example roundness or cylindrical tolerances, for pressed-on receiving parts. The shape tolerances relate in particular to the respective outer shape of the sealing region or optionally also of the entire press-on region.
Inter alia, scissors-like jointing clamps which open in a mouth-like manner at one end and are firmly connected to a drive device at the other end are known in practice for pressing pipe joints having nominal diameters DN up to 54 mm to give a seal. For larger nominal diameters DN, as a rule press chains or even press rings are used which have to be uncoupled from the coordinated drive device each time they are placed on an installation element to be pressed on.
DE 93 14 054 U1 discloses a jointing clamp for pressing pipe joints. The jointing clamp has two press levers, at one end of each of which a substantially rigid press jaw is provided and which in each case are mounted by means of an axle so as to be pivotable in opposite directions on connecting plates. When the tool is in the closed state, a substantially cylindrical press shape which is incorporated into the pressed object during pressing is formed by the two press jaws. Owing to the given dimensions of such jointing clamps, it has been found in practice that the handling is inconvenient where space is limited, in particular in the production of pipelines for household installations, and is often not possible at all in the case of preinstalled fittings close to the wall or close to the floor. In addition, particularly close to the floor, there is the danger that small objects or building site rubble may prevent complete closing of the jointing clamps, which may result in malfunction of the pipe joint. Since, in addition, the end pieces of the jointing clamp which open in a mouth-like manner can be seen only with difficulty by the operator, jointing clamps in which a special device for monitoring for complete closing of the two press jaws is provided are known.